1. Field of the Invention
This invention relates generally to a wheeled vehicle designed to turn about a vertical axis. In particular, the invention relates to powered utility riding vehicles of the type useful for aircraft servicing operations, airport passenger vehicles, lawnmowers, warehouse utility vehicles, wheelchairs, or in any vehicle where rotation-in-place steering is advantageous.
2. Description of Prior Art
Prior art vehicles are known for turning with a zero turning radius, or so called xe2x80x9cturning on the spot.xe2x80x9d U.S. Pat. No. 3,938,608 describes a vehicle with a single center mounted pivoting drive motor that is rotated about a vertical axis in order to change directions of the vehicle. The ""608 vehicle is supported with three or more swivel wheels located at equal radial distances from the center wheel. The ""608 outer profile is in the shape of a rectangle and has appendages that make close proximity maneuvering impossible next to another object such as a post or another vehicle. Furthermore, the ""608 vehicle lacks tractive force because of the single drive wheel. Furthermore, a single drive wheel must be rotated in order to change the vehicle direction, and although the single drive wheel can be turned to direct the vehicle in any direction, it does not provide directional stability for the case where a force is exerted on the vehicle from an angle to the line of intended travel. For example, a force against the ""608 vehicle at a 20xc2x0 angle to the right or left of the line of travel would force the single ""608 wheel to skid, causing loss of directional control.
The prior art concerning aircraft service vehicles has not fundamentally changed in the last fifty years. Conventional tow vehicles for aircraft, often called tractors, are typically configured with two axles, one in front, the other in the rear. The rear axle is fixed to the vehicle and provides motive force; two additional wheels are located at the front end of the vehicle, each being steerable and connected together to provide steering of the vehicle. Since there is a distance between the fixed rear drive wheels and the axis of the steerable wheels at the front end of the vehicle, a turning radius is required that far exceeds the space actually occupied by the vehicle itself. The longer the distance between front and rear axles, the larger the turning radius that is required to change directions of the vehicle. A large turning radius makes maneuvering around crowded airport ramp areas difficult and often dangerous. Operators are required to look over their shoulders in order to back up, and congestion is commonplace at airport and air service facilities. All the vehicles around an airport ramp share these common shortcomings. A need exists for a service vehicle that requires less square footage for its footprints as well as the space required for maneuvering so that operator safety and the safety of the aircraft are enhanced.
Mowing vehicles share common problems with those of aircraft service vehicles. Commercial mowers used to mow highways and large areas commonly use row-crop tractors to pull the mowers. Such tractors are designed to pull heavy loads such as plows in a straight line with few turns, but mowing requires maneuvering around obstacles such as post, rails, and curbs. Furthermore, mowing must be for ravines, ditches and on hillsides. Rolling over or tipping of such equipment is a common problem and safety hazard. A vehicle that requires no more room than it occupies in area for maneuvering and having a low center of gravity would be very advantageous for all commercial mowing applications.
A primary object of this invention is to provide a service vehicle that has enhanced maneuverability.
Another object of the invention is to provide a service vehicle that can turn on the spot and be of the smallest physical size relative to the space it occupies.
Another object of the invention is to provide a service vehicle which reduces the risk of accidents which result in damage or injury to equipment or operating personnel.
Another object of the invention is to provide a service vehicle having an outer perimeter that defines an outer imaginary cylinder that encloses any equipment or appendages mounted on the vehicle thereby enhancing its capability to maneuver the vehicle without hanging up on objects external to the vehicle.
Another object of the invention is to provide a service vehicle with structures mounted thereon for materials handling or people transport.
Another object of the invention is to provide a service vehicle that can be used for towing, pushing or handling aircraft equipment.
Another object of the invention is to provide a mowing machine that can turn on the spot and maneuver easily about obstructions.
Another object of the invention is to provide a people-moving cart for use at an airport, where the cart can turn around on the spot and be of the smallest physical size relative to the space it occupies.
The objects identified above along with other features and advantages of the invention are incorporated in a vehicle that, due to a combination of its characteristics including its shape and the configuration of its drive wheels, provides unique maneuverability and efficiency. When the vehicle is combined with a radial movable hitch to its circular frame, such combination provides for free circumferential attachment to and movement of other vehicles for transport of such vehicles with minimal space required for maneuverability and safety of operation. Such vehicles include aircraft baggage loading equipment, baggage carts, tractors and other wheeled equipment adapted for aircraft and airport operations.
The vehicle according to the invention has a frame with a perfectly round outer surface about its perimeter with no external appendages. That outer surface is characterized as a perfect, unobstructed smooth circle defined by a vertical axis of the vehicle. The vehicle has two independent drive wheels located on a horizontal axis which intersects the vertical axis. Each wheel is at exactly the same distance from the vertical axis, with each wheel having the capability to move independently and at infinitely variable speeds in either direction. Thus, the vehicle is capable to move in any direction by rotating the axis of the drive wheels perpendicular to the desired direction of travel. By applying motive force to the wheels in the appropriate direction and speed, the vehicle can turn and move in any direction perpendicular to the axis of the drive wheels within the area covered by its circumference. Rotating about the vertical axis to any radial position without changing its original footprint, the vehicle requires a true zero turning or maneuvering radius, and thus requires only the space that it occupies in which to maneuver in any direction. The xe2x80x9cfootprintxe2x80x9d is the area on the ground below the vehicle when it is at rest.
The capability to maneuver with a zero turning radius in addition to having a perfectly round and smooth perimeter with no apparatus which is mounted on the frame of the vehicle which extends beyond the outer perimeter of the frame provides for virtually unlimited directional movement and requires no maneuvering space beyond the area or footprint covered by the vehicle itself. The space required of the vehicle is no greater than that of a conventional vehicle with a drive axle and a steering axle.
One embodiment of the invention is in a vehicle capable of pulling single or multiple pieces of equipment such as trailers or various sized objects such as aircraft. In this configuration as a tow vehicle or tractor, the vehicle is equipped with a smooth outer ring including upper and lower rails which support a trolley. The trolley includes a plurality of precision wheels or rollers that are rotatably coupled to the upper and lower rails of the outer ring and enable the trolley to move freely around the entire circumference of the outer rim of the vehicle. The trolley can be rotated either manually, or through the use of a motor, for positioning the trolley to the desired position at any point about the circumference of the vehicle prior to connection to the object to be moved. Attached to the trolley or xe2x80x9ctruck assembly,xe2x80x9d via a hitch is a pivoting arm that can be stored in the vertical position perpendicular to the ground, or when in use, lowered to a position approximately parallel to the ground where it may then be attached to either a towable trailer or another object to be moved such as an airplane. The connecting arm is capable of movement about an arc vertically from its pivot point, but not laterally relative to the pivot point.
When the connecting arm is then connected to the object to be moved, and after the axis of the tow vehicle drive wheels is positioned (by operator action) perpendicular to the desired direction of movement, the tow vehicle exerts a pushing or pulling motive force against the object (e.g., trailer or airplane) being towed or pushed. The direction of travel of the towed or pushed object can be changed by adjusting the angle of the connecting arm or hitch relative to the direction of travel of the axis of the tow vehicle drive wheels. This is accomplished by rotating the axis of the drive wheels of the tow vehicle radially to any desired angle relative to the object being towed or pulled and then exerting forward or reverse power to the drive wheels. Because the trolley assembly to which the connecting arm is attached is capable of movement freely about the circumference of the tow vehicle, the angle of the connecting arm or hitch can constantly be adjusted to achieve the desired direction of travel of the object being pulled or pushed. This changing of relative angle and direction does not transmit any stress to the object being pushed or pulled, because the speeds of the drive wheels are continuously variable from zero to maximum and the trolley and arm move about the circumference of the tow vehicle with very little if any friction.
The arrangement of a substantially outer circular shape of a vehicle with a smooth and unobstructed outer perimeter in combination with two, independently variable speed bi-directional drive wheels located on a single axis through the exact center of the vehicle and mobile connecting point or hitch that is free to move about the full circumference of the vehicle working in conjunction with a perpendicularly fixed connecting bar results in a tow vehicle characterized by the ability to move omni-directionally about a given point, change directions with zero maneuvering room beyond the physical footprint of the vehicle, and push or pull other mobile vehicles with precise control. Such characteristics reduces the operating space on the ground required to move or handle an object being manipulated thus increasing operating efficiency. Safety is increased because the operator of such a vehicle, positioned directly at the center of the tow vehicle, can always be facing the direction the vehicle is moving, never having to back up and look backward.
Whether pushing or pulling another object such as an aircraft or trailer or cart, the field of vision of the operator of the tow vehicle is always facing the direction of movement of the vehicle. In operation, the operator rotates the axis of the drive wheels until it is perpendicular to the direction of the desired travel by rotating one wheel in one direction and the other in the opposite direction. Once the desired drive axle orientation is reached (perpendicular to the desired direction of travel), both wheels are given power equally, causing the vehicle to move in the direction perpendicular to the drive wheel axis of the tow vehicle axle. The vehicle being towed or pushed is then steered in the new direction and the angular attitude between the tow vehicle and the steering axle of the vehicle being towed or pushed automatically comes into an appropriate geometry as the radial hitch travels about the perimeter of the tow vehicle.